Summary Cochlear implants (CIs) are neuroprosthetic devices that can restore meaningful hearing to the profoundly deaf. However, while some recipients can understand speech soon after implantation, others require significant time and practice with the device to attain useful phoneme and speech recognition. The causes of this variability in both initial performance and time-to-peak performance are poorly understood. Elucidating the mechanisms of neuroplasticity that underlie a patient's ability to reinterpret the implant signal can provide insight into how the brain adapts to the device and where it goes wrong. The proposed project focuses on investigating these underlying neural mechanisms in a rodent model of cochlear implant use. The goal of this proposal is to investigate the neurophysiological basis of the variability in initial performance and in time-to-peak performance with a CI. First, I will show that deaf rats can learn to use a CI to report frequency percepts and ask how different degrees of frequency mismatch between the pre-CI acoustic stimuli and CI stimuli affect behavioral performance on the first day of stimulation. I will then examine the role of auditory cortex in learning with the CI, asking how cortical responses to different CI channels relate to behavioral recognition of the different CI channels. My preliminary data demonstrate that rats can use a CI to report frequency percepts and that micro-electrocorticography arrays are a feasible technique for chronic studies of auditory cortical processing in freely moving rats. I anticipate that these studies will contribute considerable understanding of the neural mechanisms of CI use and differences in central auditory processing that might reflect differences in individual perceptual gains.